Materials that exhibit redox pseudocapacitance are promising alternatives to high-surface-area carbons as charge-storing materials in next-generation electrochemical capacitors (ECs). While carbons have the inherent electronic conductivity required to support high-power operation, most pseudocapacitive materials, including transition metal oxides (e.g., MnOx, FeOx) and electroactive polymers, are either poorly conductive or their conductivity varies significantly as a function of charge state. Thus, pseudocapacitive materials are typically combined with conductive carbons to yield practical electrodes. At the Naval Research Laboratory we pioneered an electrode design in which pseudocapacitive oxides, such as MnOx and FeOx, are applied as nanoscale coatings onto ultraporous, x–y–z scalable carbon nanofoam substrates [1,2]. The structural characteristics of these 3D electrode designs yield enhanced performance in EC applications, particularly in terms of geometric area-normalized capacitance. While continuing to develop and transition these next-generation electrode architectures, we have also found that more subtle design factors, such as nanoscale order/disorder in the metal oxide coating [3] and the physicochemical nature of the carbon–metal oxide interface, can have a significant impact on electrochemical performance. For fundamental investigations of such phenomena, we use planar pyrolytic-carbon substrates to mimic the surface properties of 3D carbon, but in forms that are more readily characterized by conventional surface spectroscopy and scanning-probe microcopy. We apply nanoscale pseudocapacitive oxides and redox polymers to these planar carbon films and explore how the physical, chemical, and electronic structure of the resulting interface as carbon meets pseudocapacitive material sways electrochemical properties. Lessons learned from these model interfaces are readily translated to improved performance in practical 3D electrode architectures.

Understanding pseudocapacitive charge storage from fundamental interfacial processes to 3D electrode design

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.